The cells involved in bone resorption and bone formation, e.g., osteoclasts, osteoblasts and osteocytes will be studied in bone tissue maintained in organ culture. Their activity will be assessed by quantitative ultrastructural morphology and these data will be correlated with biochemical data on the same tissue. We will test the effects of regulatory hormones such a parathyroid hormone, vit. D metabolites and calcitonin, as well as other agents influencing bone metabolism, such as osteoclast activating factor (OAF), prostaglandins, nutrients and ions. These studies will form the basis for investigation of the pathology of bone cells and the pathogenetic mechanisms in bone disorders, such as osteoporosis in leukemics, osteogenesis imperfecta osteopetrosis, juvenile idiopathic osteoporosis, renal osteodystrophy.